I preface this by saying that I have never ever ever cheated, and hate the fuckers that do. And over the years have been responsible for sending Q3 cheaters to the master ban list at PB. The Q3 clan and the last cod clan I belonged to were diligent in identifying and on a regular basis sending cheaters to the master ban list, so this is where my limited knowledge comes from...
Quake 3, although the best game ever made

is the father of all that we see as good and evil! Based on the Q3 engine COD UO is just quake 3 in a low cut black dress with high heels

, fishnet stockings, and lipstick. Infinity Ward did a great job, but its really just Quake3 only you can't jump as high and instead of a rail gun its a sniper rifle!
Extentions for binds were widely exposed by the engine and used and accepted in the community. Rocket jumps - combination of look down, shoot rocket, jump... strafe/jump "exploit" would be bound to key like the binds used to say "Took you long enough". PB and TWL really limit most of 'fun' stuff from Q3, and lock down the binds and settings you can use. It would be cool to be able to press a bind to switch to panzerfaust, shoot it, then switch back to your mp44, in an instant, but alas big brother pb doesn't think its a good idea... not realistic or something.
Field of View is another example. In Q3 you could change your field of view to any number (up to 359 degrees - eyes in the back of your head) I liked 110 myself, good peripheral and you could still see what you were shooting at. Any more and it became to hard to aim... UO - 90... You would be surpised how important the extra 20 degrees of FOV is!
Aimbot's were quite prevelent in the days up to the advent of PB. A bot would connect to the server and have like 200 kills and no deaths.

A server of 30 people would be destroyed and everyone would have to leave...Can't count the number of times that happened! PB was long overdue and saved online gaming in my opinion. The Q3 engine exposes the development tags to build the hacks, all you need is some knowledge and basic coding. In fact, the AI shipped had much of the code for the hacks. PB does a pretty good job of verifying 'stock' parameters but there is always some dilweed...
Wallhack - they typically just provide information about enemy location. As if there are no 'walls' Just knowing location of the enemy can be a huge advantage. I haven't seen anyone able to shoot through the wall, just knowing someone is around the corner is the advantage. I have seen a number of variations through PB screenshots, and you can find them on the net. Some like wireframe hud, or some marker like a red dot over the enemies head... lots of em.
Exploits many - places you can shoot someone but can't be shot or you can see stuff you shouldn't be able to. Map exploits like going underneath the map etc. ie Hill at Kursk is a map exploit...
sh